1. Field of the Invention
The present invention relates to a reagent composition and a testing piece for measuring a specific component in a liquid sample, and more particularly to a reagent composition, a testing piece, and an assay kit for measuring a specific component, whereby the influence of a reducing substance such as ascorbic acid is eliminated in a liquid sample such as serum, plasma, urine, or culture medium.
2. Description of the Related Art
Various substances having reducing action are contained in liquid samples such as serum, plasma, urine, or culture medium. Examples of such reducing substances include ascorbic acid and uric acid.
During measurement using a testing piece that detects, for example, glucose or occult blood based on a redox reaction, the greater the concentration of reducing substances such as ascorbic acid in the liquid sample, the greater their influence in lowering the measured value of the analyte.
Many methods are thus far known for avoiding the influence of such reducing substances.
For example, Japanese Patent Application Laid-Open No. 52-150692, discloses a method in which such effects are avoided by using ascorbic acid oxidase. A problem in this method, however, is that the ascorbic acid oxidase is expensive and unstable.
Japanese Patent Application Laid-Open No. 59-230161 discloses a method in which copper ions are used to oxidize ascorbic acid. A problem in this method, however, is that the metal ions directly oxidize the redox dye and cause it to color.
Japanese Patent Application Laid-Open No. 56-151358 discloses a method for oxidizing ascorbic acid using an iodate. A problem in this method, however, is that the oxidation properties are too strong, and that the iodine directly oxidizes the redox dye, causing it to color.
In Japanese Patent Application Laid-Open No. 59-187266 (Japanese Patent Publication No. 1-41223), an iron (II) or iron (III) complex of a compound represented by the formula R.sub.1 R.sub.2 NCH.sub.2 COOH or R.sub.3 R.sub.4 NXNR.sub.5 CH.sub.2 COOH or an iron (II) or iron (III) complex of gluconic acid is added to eliminate the ascorbic acid during the measurement of components in body fluids. A problem in this method, however, is that the metal ions directly oxidize the redox dye, causing it to color.
In Japanese Patent Application Laid-Open No. 59-193354 (Japanese Patent Publication No. 4-18630), an iron (III) complex of a polycarboxylalkylamine derivative is added to a composition for detecting peroxide active materials. A drawback in this method, however, is that the metal ions directly oxidize the redox dye, causing it to color.
To remedy the aforementioned drawbacks, it has been developed a composition for detecting a peroxide active material (Japanese Patent Application Laid-Open No. 6-148168, U.S. Pat. No. 5,439,827), comprising an organic hydroperoxide, a chromogen, and an iron complex represented by the general formula: (OOC--X--COO).sub.3 Fe!Me.sub.3 wherein X is an alkylene group and M is a monovalent cation. The use of this composition allows the effects caused by reducing substances to be effectively eliminated, but the effects are temperature-dependent. When, for example, measurements are undertaken as the temperature is adjusted to around 37.degree. C. in a device, the measurements can be accurate, but there is still room for improvement during visual measurements while viewing a calorimetric chart at room temperature. There is also room for improving the storage stability of the composition itself.